That sounds pretty nice overall. A couple spots (like the terribilis) were a tad dramatic for my tastes, but it might be justified. The score and recording definitely had some differences though, maybe the choir was singing from an different revision?

I also think, if you can write solid polyphony (which it seems like you can, and I wish I could) there is a good opportunity for composing new polyphony to be used in alteration with an old chant. There are lots of chants that most people never sing (like from Cantus Varii and Cantus Selecti, available in the CMAA resources) which could make for really good pieces if cleverly arranged with some well crafted polyphony. Just my opinion though.

yes You were right, I am uploading the correct version below, and Your opinion the need to write polyphony is absolutely correct